1. Field of the Invention
This invention generally relates to a torque converter. More specifically, the present invention relates to a torque converter having a lock-up clutch installed therein.
2. Background Information
Torque converters usually include a fluid coupling mechanism for transmitting torque between the crankshaft of an engine and the input shaft of an automatic transmission. In recent years, to improve fuel efficiency, some torque converters have included lock-up devices that, upon reaching predetermined operating conditions, lock-up the torque converters so that power from the crankshaft of an engine is directly transmitted to the automatic transmission, bypassing the fluid coupling device. Upon engagement, lock-up devices often cause a shudder, or vibration. Further, while engaged, the lock-up device is subject to vibrations caused by sudden acceleration, or deceleration, or other vibration including circumstances associated with internal combustion engines. Consequently, a torsional vibration dampening apparatus is typically employed in a lock-up mechanism to dampen vibration.
A torque converter has three types of runners (impeller, turbine, stator) located inside for transmitting the torque by means of an internal hydraulic oil or fluid. The impeller is fixedly coupled to the front cover that receives the input torque from the power input shaft. The hydraulic chamber formed by the impeller shell and the front cover is filled with hydraulic oil. The turbine is disposed opposite the front cover in the hydraulic chamber. When the impeller rotates, the hydraulic oil flows from the impeller to the turbine, and the turbine rotates. As a result, the torque is transmitted from the turbine to the main drive shaft of the transmission.
The lock-up clutch is disposed in the space between the front cover and the turbine. As mentioned above, the lock-up clutch is a mechanism to directly transmit the torque between the crankshaft of the engine and the drive shaft of the transmission by mechanically coupling the front cover and the turbine. The lock-up clutch includes primarily a piston and an elastic coupling mechanism to connect the piston to the members on the power output side of the turbine. The piston is disposed to divide the space between the front cover and the turbine into a first hydraulic chamber on the front cover side and a second hydraulic chamber on the turbine side. As a result, the piston can move close to and away from the front cover by the pressure difference between the first hydraulic chamber and the second hydraulic chamber. A friction joining member covered by friction facing is formed on the outer periphery of the front cover on the axial surface facing the piston. When the hydraulic oil in the first hydraulic chamber is drained and the hydraulic pressure in the second hydraulic chamber increases in pressure, the piston moves toward the front cover side. This movement of the piston causes the friction facing of the piston to strongly press against the friction surface of the front cover.
The elastic coupling mechanism functions as a torsional vibration dampening mechanism to dampen vibration in the lock-up clutch. The elastic coupling mechanism includes, for example, a drive member fixedly coupled to the piston, a driven member fixedly coupled to the turbine side, and an elastic member, such as one or more coil springs, disposed in between the drive member and the driven member to enable torque transmission.
When the lock-up clutch is engaged, the hydraulic oil in the first hydraulic chamber is drained from its inner circumferential side and the hydraulic oil is supplied to the second hydraulic chamber. As a result, the hydraulic pressure in the second hydraulic chamber becomes greater than the hydraulic pressure in the first hydraulic chamber. This pressure differential between the first and second hydraulic chambers causes the piston to move toward the front cover. During the movement of the piston, the hydraulic oil in the second hydraulic chamber sometimes flows through the gap between the friction facing and the friction surface of the front cover into the first hydraulic chamber. In this case, the hydraulic pressure in the second hydraulic chamber does not become large enough, and the moving speed of the piston becomes slower.
In view of the above, there exists a need for a torque converter, which overcomes the above mentioned problems in the prior art devices. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.